1. Field of the Invention
The present invention relates to a laser ablative recording material, and a laser ablative record of an image formed through imagewise heating of the laser ablative recording material.
2. Description of the Related Art
Recently, a thermal transfer system forming an image by imparting an electric signal to a thermal print head has become more popular. A method of forming an image by the use of a laser in place of the thermal print head was on the other hand developed, and is expected to become more popular along with the tendency toward a higher laser output.
A recording material for laser recording contains a material having a strong absorption in the laser wavelength region, and this absorbing material converts optical energy into thermal energy, and brings about effects similar to those available by the use of a thermal print head. Use of a laser, unlike the use of a thermal print head, permits heating without contact with a recording material, thus providing an advantage of the image surface free from flaws. Because of the possibility to stop down a laser beam, there is provided another advantage of improving image resolution.
A method for forming an image using a high-output laser known as the dye ablation has recently been developed. Japanese Unexamined Patent Publications Nos. 7-164,755, 7-149,063, and 7-149,065 (corresponding to U.S. Pat. No. 5,330,876, U.S. Pat. No. 5,401,618 and U.S. Pat. No. 5,459,017) disclose recording materials applicable in this method, and Japanese Unexamined Patent Publications Nos. 8-48,053 and 8-72,400 (corresponding to U.S. Pat. No. 5,521,629 and U.S. Pat. No. 5,574,493) disclose imaging apparatuses used in this method. Image recording based on the ablation method is accomplished by irradiating a laser from a dye layer side onto a recording material having a dye layer comprising an image dye, a material having absorption in the laser wavelength region (infrared-absorbing material) and a binder formed on a support. On the spot to which the laser beam has been irradiated, a sharp local change takes place in an image forming layer under the effect of energy from the laser, and this drives away the material from the layer. According to the aforesaid patent publications, this local change is not a perfectly physical change such as melting, evaporation or sublimation, but a kind of chemical change such as bond-breaking, and is believed to be a complete, not partial, removal of the image dye.
Usefulness of this dye ablation imaging method largely depends upon removal efficiency of the imaging dyes upon laser exposure. As a scale representing this efficiency, the minimum concentration value (Dmin) of the laser exposure portion is employed. A smaller value of Dmin is suggested to lead to a higher dye removing efficiency, and provision of a laser ablative recording material having a small Dmin is demanded for.
A recording material used for dye ablation imaging method is produced by applying and drying a material solved or dispersed in an organic solvent on a support such as polyethylene terephthalate or aluminum on which a surface is generally treated properly. Roller coating, wire doctor coating, etc. are used as a coating method. When a coating liquid of a low viscosity (about 10 cp or below) is applied, those methods raise problems that the dried surface becomes Benard Cells' state or the film thickness profile of the image forming layer becomes uneven due to temperature and humidity controlled air used during drying.
If a recording material with such unevenness defects is used as an output sensing material for a platemaking process, the unevenness on the recording material emerges as density unevenness when printed on a plate. When a recording material with unevenness defects is used as a printed plate, it causes deviations of printing durability. Laser ablative recording materials need particularly an even surface state and an even film thickness profile because a coloring agent at unexposed portions to laser beam creates a maximum density.
Meanwhile, fluorine-containing surfactants were recently found useful for specific usage. For example, Japanese Patent Publication (KOKOKU) No. Heisei 8-3,630 discloses fluorine-containing surfactants for photosensitive flat printing plates; Japanese Unexamined Patent Publication (KOKAI) sets forth use of fluorine-containing surfactants when a liquid of specific mixed solvents is coated with a coating die of a slide hopper type, extrusion type, or curtain hopper type. The specification of U.S. Pat. No. 5,380,644 sets forth use of fluorine-containing surfactants in photosensitive thermal sensitive materials containing organic silver salt or thermal sensitive materials. However, nothing describes use of fluorine-containing surfactants in laser ablation recording materials.